A glass substrate for a liquid crystal display element has been considered for making the substrate thin in order to eliminate double image of display and to accomplish a light weight device. However, in the case where a glass substrate is individually carried to a producing process, thinning of the substrate is limited to 0.7 mm in a mass production level because of problems, such as fragility, liability to breakage. For these reasons it is difficult produce liquid crystal display elements in which large glass (300 mm.times.300 mm and above) whose thickness is 0.5 mm or 0.3 mm.
Meanwhile, a liquid crystal display element in which a plastic substrate is used has been developed instead of a glass substrate. As to a producing method for the plastic substrate, for example, Japanese Unexamined Patent Publication No. 3-5718/1991 (Tokukaihei 3-5718) discloses a method of independently carrying a sheet-like plastic substrate or a method of successively carrying a roll-like plastic substrate.
However, in both cases where the substrate is individually carried and the roll-like substrate is successively carried, it is more difficult to produce a liquid crystal display element in which a plastic substrate is used compared to a liquid crystal display element in which a glass substrate is used because of small stiffness, namely, no body, a low heat deformation temperature, liability to damage due to low surface hardness, liability to occurrence of deformation such as warpage, expansion and shrinkage during heat treatment.
Therefore, for example, Japanese Unexamined Patent Publication No. 60-41018/1985 (Tokukaisho 60-41018) discloses a method of producing a liquid crystal display element by carrying a plastic substrate to processes with it fixed to a frame, and Japanese Unexamined Patent Publication No. 58-147713/1983 (Tokukaisho 58-147713) discloses a method of producing a liquid crystal display element by contact-bonding a circumferential edge section of a plastic substrate to a carrier so as to cut the contact-bonded section.
In addition, the above-mentioned Japanese Unexamined Publication No. 3-5718/1991 (Tokukaihei 3-5718) also discloses a method of producing a liquid crystal display element by laminating polymeric resin which becomes a plastic substrate on a mold-releasing film.
The mold-releasing film is formed by applying a silicone-type resin as a mold-releasing agent to a film which is a carrier.
Here, the silicone-type resin, for example, silicone is used for various applications as a general mold-releasing agent, and it is sorted into oil-type, paste-type, solution-type, baking-type, emulsion-type, water-soluble-type, spray-type, etc. For example, in order to improve releasability from a sealing sticky surface, the silicone as a mold-releasing layer is used for a surface of sealing release paper, and is used as a mold-releasing agent for easily releasing moldings from a metal mold at the time of forming resin, for example. Silicone which is used as a mold-releasing agent has no adhesion properties itself, or if the silicone has adhesion properties, it is used after its adhesion is reduced.
However, in the producing method with the plastic substrate fixed to the frame, the plastic substrate is deformed in the frame, so it is difficult to maintain evenness of the surface. In this case, various printing equipments, light exposure equipments, etc. during a process for producing a liquid crystal display element require, a special stage-type design, for example, so as to support evenness in the frame. This increases cost of the equipments and this has problems, such as incompatibility with a glass substrate.
On the contrary, in the method of producing a liquid crystal display element by laminating polymeric resin which becomes a plastic substrate on a mold-releasing film, there exist the following problems.
(1) Cost is high because a carrier such as a mold-releasing film is used only once.
(2) Stiffness of a carrier such as a mold-releasing film is low and carrying to processes is not smoothly carried out.
(3) Producing processes, equipments and conditions which can be used are greatly limited.
Particularly in a plastic substrate with flexibility, deformation is liable to occur along a hole and a channel of an absorption stage depending upon its material and thickness. For this reason, failure of printing and failure of an orientation process as well as catching by a print of an offset printer occur, and besides, at the time of temporary drying immediately after printing, a substrate is bent by heat on a hot plate, for example, namely, the substrate shows dance-like movement, so stable drying cannot be carried out.
(4) Stable carrying cannot be performed from a point of adhesion because of low adhesion of a mold-releasing film to polymeric resin, and especially, in the case of heating treatment, (a) bubbles on the interface between the mold-releasing film and the polymeric resin, or (2) partial peeling occurs, so the subsequent processes cannot be carried out.